Nanotube modified solder thermal intermediate structure, systems, and methods

ABSTRACT

An apparatus and system, as well as fabrication methods therefor, may include a thermal intermediate structure with metal decorated carbon nanotubes incorporated in solder.

TECHNICAL FIELD

The subject matter relates generally to thermal intermediate structures,systems, and methods used to assist in transferring heat from oneelement or body, such as a circuit, to another, such as a heat sink.

BACKGROUND INFORMATION

Electronic components, such as integrated circuits, may be assembledinto component packages by physically and electrically coupling them toa substrate. During operation, the package may generate heat which canbe dissipated to help maintain the circuitry at a desired temperature.Heat sinks, including heat spreaders, may be coupled to the packageusing a suitable thermal intermediate structure to assist intransferring heat from the package to the heat sink.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a thermal intermediate structureplaced between an electronic circuit die and a heat sink according tovarious embodiments;

FIGS. 2A and 2B are views in enlarged and schematic form of anembodiment of carbon nanotubes used in the thermal intermediatestructure;

FIG. 3 is a view showing randomly aligned carbon nanotubes in solder;

FIG. 4 illustrates a process for alignment of carbon nanotubes for usein the thermal intermediate structure;

FIG. 5 is a view showing a thermal intermediate blank cut from therolled billet of FIG. 4;

FIGS. 6–7 are flow charts illustrating methods according to variousembodiments; and

FIG. 8 is a depiction of a computing system according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description of various embodiments, referenceis made to the accompanying drawings that form a part hereof, and inwhich are shown by way of illustration, and not of limitation, specificembodiments in which the subject matter may be practiced. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. The embodiments illustrated are describedin sufficient detail to enable those skilled in the art to practice theteachings disclosed herein. Other embodiments may be utilized andderived therefrom, such that compositional, structural, and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure. The following detailed description, therefore, isnot to be taken in a limiting sense.

Examples and embodiments merely typify possible variations. Individualcomponents and functions are optional unless explicitly required, andthe sequence of operations may vary. Portions and features of someembodiments may be included in or substituted for those of others. Thefollowing description is, therefore, not to be taken in a limitingsense.

FIG. 1 is a cross-section elevation view of an apparatus 10 according tovarious embodiments. Apparatus 10 includes a package substrate 12, a die14 and a thermal management aid such as a heat sink or an integral heatspreader 16 which is mounted adjacent the die 14 and separated from itby a gap.

In an embodiment, the substrate of die 14 is made of silicon and hasfrontside and backside surfaces. The die 14 also has an integratedcircuit 20 and solder bump contacts 22 on the frontside surface. Thecontacts 22 connect with contact pads (not shown) on the upper surfaceof package substrate 12. In some embodiments, the contacts 22 aremanufactured according to a commonly used controlled collapse chipconnect (C4) process.

In use, electric signals and power are provided to the integratedcircuit 20. Operation of the integrated circuit 20 causes heating of die14. Heat is transferred from the integrated circuit 20 through thesubstrate of die 14 to the heat spreader 16 through a thermalintermediate structure 24 interposed in the gap between them. In anembodiment a buffer layer 18 is interposed between thermal intermediatestructure 24 and heat sink 16.

Carbon nanotubes have a coefficient of thermal conductivity along theirlongitudinal axis which is relatively high relative to theirconductivity along a path oriented orthogonal to the longitudinal axis.The thermal conductivity of carbon nanotubes along their longitudinalaxes is substantially higher than that of other materials used forthermal intermediates. The thermal conductivity of multi-wallednanotubes is about 3000 to 4000 W/m-K and theoretically about 6000 W/m-Kfor single walled nanotubes.

In an embodiment, the thermal intermediate structure 24 comprises aplurality of either multi-walled or single walled carbon nanotubes or acombination of both single and double walled nanotubes which are blendedwith solder. In an embodiment, the carbon nanotubes are chemicallybonded to the solder. In an embodiment, the carbon nanotubes aredistributed through a matrix of solder and make up a volume percentagethe total less than about 5% to 50% of the volume of the composition byweight.

In an embodiment, the solder material is indium which has a thermalconductivity of at least about 85 W/mK. While in one embodiment a solderformed of an indium alloy could have a high thermal conductivity, othersolder alloys generally have thermal conductivities of 30 W/mK or lower.

Forming a blend of carbon nanotubes and solder or a distribution ofcarbon nanotubes in a solder matrix is complicated due to the lowwetting of nanotubes to most solders. In one embodiment, chemicalbonding of the solder to carbon nanotubes of the plurality of carbonnanotubes is facilitated by pre-coating some of the carbon nanotubesprior to blending them with the molten solder.

In one embodiment, prior to the blending of the carbon nanotubes withthe solder, at least some of the carbon nanotubes 28 of the thermalintermediate structure 24 are pre-coated or partially pre-coated with ametal is selected from the group consisting of gold, platinum, silver orpalladium and alloys comprising one or more of gold, platinum, silverand palladium, or other suitable metals or alloys, by physicaldeposition or sputtering methods which are known.

In one embodiment, the coated nanotubes 28 are also referred to asdecorated with the coating metal. The metal decorations on the nanotubesprovide a wetting contact between the nanotubes and the solder toimprove the bond between the solder and the nanotubes and further reducethe contact thermal resistance between nanotubes of the thermalintermediate structure 24 and either the surface of die 14 or of heatspreader 16.

In one embodiment, incorporation of metal particles 32 at various pointsdistributed along the body of some nanotubes 28 of the plurality ofnanotubes should improve the wetting of the nanotubes with soldersurrounding those nanotubes. In one embodiment shown in FIG. 2A, a knownprocess for decorating carbon nanotubes with gold, platinum, palladiumor silver involves an initial refluxing of nanotubes with nitric acid toopen closed tips of the tubes 28 and to create acid sites 30 on thesurface of nanotubes 28 to act as nucleation centers for metal ions.Refluxing the nanotubes in the presence of a reducing agent such asHAuCl₄ results in FIG. 2B with gold particles 32 forming at thenucleation sites to produce decorated carbon nanotubes. Similarly, in anembodiment, a reducing agent H₂PtCl₆ is used to decorate the nanotubeswith platinum. Similar processes can also be used to incorporatepalladium or silver with acid opened nanotubes.

The acid sites 30 which receive the metal decorations 32 are understoodto be generally dispersed over the body of the nanotubes 28 rather thanalong fault lines as would be expected in the case of metal decorationof graphite crystals, for example.

In one embodiment, electrochemical means of coating nanotubes with metaldecorations can be utilized. In one embodiment, coating a second metalon the nanotube for alloying purposes as part of the metal decorationprocess can be utilized.

In one embodiment, other physical methods such as sputtering can be usedto produce metal coated carbon nanotubes.

Decorating the carbon nanotubes 28 with metals 32 to improve the wettingof the nanotubes for forming a chemical bond between the solder 28 andthe decorated nanotubes. In one embodiment, alignment of the nanotubesalong the shortest heat transfer path will contribute to maximizing thethermal performance of the thermal intermediate structure 24. In FIG. 1,the shortest path for heat flow from die 14 to heat spreader 16 is alongpaths perpendicular to the surfaces of die 14 and heat spreader 16 whichengage thermal intermediate structure 24.

In FIG. 3, a portion of a thermal intermediate structure 24 according toan embodiment is shown in enlarged schematic form with a plurality ofcarbon nanotubes 28 somewhat randomly oriented in the matrix of solder29 into which they are mixed.

In one embodiment, some of the carbon nanotubes 28 of the plurality ofcarbon nanotubes are to be aligned in an x, y plane by successiverolling and folding operations performed on the solder 29 and carbonnanotube 28 composite material.

In FIG. 4, a billet of indium solder which has incorporated within it aplurality of single walled nanotubes or of multiple walled nanotubes, isrolled or extruded along an axis 33 to align at least some nanotubes 28of the plurality of nanotubes with each other and generally parallel toaxis 33 as shown in FIG. 4 forming a billet 35 of solder material withblended nanotubes generally aligned with each other and parallel to axis33.

Indium is well adapted to such rolling and folding operations because itis soft and easily workable. The mixture of nanotubes 28 which areincorporated into the solder 29 do not materially detract from themechanical workability of billet 35. In an embodiment, the density ofnanotubes 28 in the solder 29 is less than about 5 to 30% by volume andis in some cases up to 50% by volume. In FIG. 5, a thermal intermediateblank 38 sliced from billet 35 of FIG. 4 along one of a series oftransverse cutting lines formed at one of a series of longitudinalslicing points 36, is shown after being rotated by 90° from itsalignment illustrated in FIG. 4. After a plurality of blanks 35 ofsolder/carbon nanotube composite are formed, the thin sections or blanks35 are bonded together to achieve orientation of some of the pluralityof carbon nanotubes in the z axis, normal to the heat sink 16 surfaceand the surface of die 14, for improved heat flow between the die andheat sink. One or more of such blanks 38 make up the thermalintermediate structure 24.

In one embodiment, extrusion or pultrusion of a rolled indium billet 35is followed by slicing and rotating the slice to provide orientation ofa high number of carbon nanotubes of the plurality of carbon nanotubes28 in the z-axis.

Some embodiments include a number of methods. For example, FIG. 6 is aflow chart illustrating several methods according to variousembodiments. Thus, a method 611 may (optionally) begin at block 621 withforming a billet 35 of solder 29 incorporating a plurality of carbonnanotubes 28 therein which are chemically bonded to the solder. Themethod includes, at block 631, aligning a substantial percentage of thecarbon nanotubes with an axis of the billet by successive rollingoperations. In one embodiment in the method at block 631, the aligning asubstantial number of the carbon nanotubes includes working the billetby a process selected from the group consisting of rolling extruding orpultruding to align some carbon nanotubes 28 of the plurality of carbonnanotubes with axis 33 (FIG. 4) along which the working of the billet 35occurs.

In one embodiment, the method includes, in block 641, slicing the billetperpendicular to the axis 32 into thermal intermediate blanks 38 havinga thickness substantially less than their length or width. The thermalintermediate blanks 38 are then assembled into a thermal intermediatestructure 24 having a substantial percentage of the carbon nanotubes ofplurality of carbon nanotubes 28 aligned.

In an embodiment, in block 651, the thermal intermediate structure 24 isinterposed in a gap between a die 14 and a heat sink 16. In anembodiment, the gap between the die and the heat sink is less than orequal to about 20 microns. In other embodiments the gap may be as largeas from about 150 to about 250 microns or as small as 5 microns.

FIG. 7 is a flow chart of a method 710 illustrating several methodsaccording to various embodiments. Thus, method 710 may (optionally)begin at block 721 with forming a thermal intermediate structurecomprised of a plurality of metal decorated carbon nanotubes 28 blendedinto a solder material 29 with at least some of the plurality of carbonnanotubes 28 substantially aligned with an axis 32 of billet 35.

In an embodiment, the method includes, in block 731, coupling a firstsurface of the thermal intermediate structure to a surface of a heatsink with the surface of the thermal intermediate structure orientedsubstantially perpendicular to the surface of the heat sink. In oneembodiment, the method includes, in block 741, coupling a second surfaceof the thermal intermediate structure to a surface of the heat source

In an embodiment, the process in block 731 of coupling a first surfaceof the thermal intermediate structure 24 to a surface of a heat sink 16also comprises forming a solder bond between the surface of the heatsource 14 and the second surface of the thermal intermediate structure24. In one embodiment, the process in block 741 of coupling a secondsurface of the thermal intermediate structure 24 to a surface of theheat sink 16 also comprises forming a solder bond between the surface ofthe heat sink 16 and the first surface of the thermal intermediatestructure 24.

FIG. 8 is a depiction of a computing system according to an embodiment.One or more of the embodiments of apparatus with one or more dies 14having a thermal intermediate structure 24 interposed between the diesurface and the heat sink 16 and comprising a plurality of carbonnanotubes 28, some of which are decorated with metal 32, the pluralityof carbon nanotubes blended with solder 29 may be used in a computingsystem such as a computing system 800 of FIG. 8. The computing system800 includes at least one processor (not pictured), which is enclosed ina microelectronic device package 810, a data storage system 812, atleast one input device such as a keyboard 814, and at least one outputdevice such as a monitor 816, for example. The computing system 800includes a processor that processes data signals, and may include, forexample, a microprocessor available from Intel Corporation. In additionto the keyboard 814, an embodiment of the computing system includes afurther user input device such as a mouse 818, for example.

For the purposes of this disclosure, a computing system 800 embodyingcomponents in accordance with the claimed subject matter may include anysystem that utilizes a microelectronic device package, which mayinclude, for example, a data storage device such as dynamic randomaccess memory, polymer memory, flash memory and phase change memory. Themicroelectronic device package can also include a die that contains adigital signal processor (DSP), a micro-controller, an applicationspecific integrated circuit (ASIC), or a microprocessor.

Embodiments set forth in this disclosure can be applied to devices andapparatus other than a traditional computer. For example, a die 14 canbe packaged with an embodiment of the thermal intermediate structure 24,and placed in a portable device such as a wireless communicator or ahand held device such as a personal data assistant or the like. Anotherexample is a die 14 that can be coupled to a heat sink 16 with anembodiment of the thermal intermediate structure 24 and placed in adirigible craft such as an automobile, a watercraft, an aircraft or aspacecraft.

The apparatus 10, substrate 12, die 14, heat spreader 16, integratedcircuit 20, solder bumps 22 thermal intermediate structure 24 and metaldecorated, aligned nanotubes 28 may all be characterized as “modules”herein. Such modules may include hardware circuitry, and/or a processorand/or memory circuits, software program modules and objects, and/orfirmware, and combinations thereof, as desired by the architect of theapparatus 10 and system 900, and as appropriate for particularimplementations of various embodiments. For example, such modules may beincluded in a system operations simulation package, such as a softwareelectrical signal simulation package, a power usage and distributionsimulation package, a thermo-mechanical stress simulation package, apower/heat dissipation simulation package, and/or a combination ofsoftware and hardware used to simulate the operation of variouspotential embodiments.

It should also be understood that the apparatus and systems of variousembodiments can be used in applications other than for coupling and heattransfer between die and heat sinks and thus, these embodiments are notto be so limited. The illustrations of apparatus 10 and system 800 areintended to provide a general understanding of the elements andstructure of various embodiments, and they are not intended to serve asa complete description of all the features of compositions, apparatus,and systems that might make use of the elements and structures describedherein.

Applications that may include the novel apparatus and systems of variousembodiments include electronic circuitry used in high-speed computers,communication and signal processing circuitry, data transceivers,modems, processor modules, embedded processors, and application-specificmodules, including multilayer, multi-chip modules. Such apparatus andsystems may further be included as sub-components within a variety ofelectronic systems, such as televisions, cellular telephones, personalcomputers, workstations, radios, video players, vehicles, and others.

It should be noted that the methods described herein do not have to beexecuted in the order described, or in any particular order. Moreover,various activities described with respect to the methods identifiedherein can be executed in serial or parallel fashion.

Although specific embodiments have been illustrated and describedherein, it should be appreciated that any arrangement calculated toachieve the same purpose may be substituted for the specific embodimentsshown. This disclosure is intended to cover any and all adaptations orvariations of various embodiments. It is to be understood that the abovedescription has been made in an illustrative fashion, and not arestrictive one. Combinations of the above embodiments, and otherembodiments not specifically described herein will be apparent to thoseof skill in the art upon reviewing the above description. Thus, thescope of various embodiments includes any other applications in whichthe above compositions, structures, and methods are used.

It is emphasized that the Abstract of the Disclosure is provided tocomply with 37 C.F.R. §1.72(b), requiring an abstract that will allowthe reader to quickly ascertain the nature of the technical disclosure.It is submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims. In addition, inthe foregoing Detailed Description, it can be seen that various featuresare grouped together in a single embodiment for the purpose ofstreamlining the disclosure. This method of disclosure is not to beinterpreted as reflecting an intention that the claimed embodimentsrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed embodiment. Thus the followingclaims are hereby incorporated into the Detailed Description, with eachclaim standing on its own as a separate preferred embodiment. In theappended claims, the terms “including” and “in which” are used as theplain-English equivalents of the respective terms “comprising” and“wherein,” respectively. Moreover, the terms “first,” “second,” and“third,” etc. are used merely as labels, and are not intended to imposenumerical requirements on their objects.

1. Apparatus, comprising: a die; a heat spreader; and a thermalintermediate material comprised of a plurality of carbon nanotubesblended with solder, the thermal intermediate material interposed in agap between the die and the heat spreader, wherein some of the carbonnanotubes of the plurality of carbon nanotubes are chemically bonded tothe solder.
 2. The apparatus of claim 1, wherein the some of carbonnanotubes of the plurality of carbon nanotubes are pre-coated with ametal prior to blending with the solder.
 3. The apparatus of claim 1,wherein some of the carbon nanotubes are decorated with metal.
 4. Theapparatus of claim 2, wherein the metal is platinum.
 5. The apparatus ofclaim 2 wherein some of the carbon nanotubes are pre-coated with a metalto wet the solder to bond it to the carbon nanotubes.
 6. The apparatusof claim 2, wherein the metal is selected from the group consisting ofgold, platinum, silver and palladium and alloys comprising one or moreof gold, platinum, silver and palladium.
 7. The apparatus of claim 1,wherein some of the carbon nanotubes are aligned in the thermalintermediate material along the heat flow path between the die and theheat spreader.
 8. The apparatus of claim 1 wherein the nanotubes arerandomly oriented in the thermal intermediate material and have averagelengths less than about 10 percent of the gap between the die and theheat spreader.
 9. The apparatus of claim 1 wherein the solder is indium.10. The apparatus of claim 1: wherein the thermal intermediate materialcomprises a matrix, wherein the matrix exhibits a phase change betweenabout 100° C. and about 230° C.; and wherein the thermal intermediatematerial includes a distribution of the carbon nanotubes in the matrixhaving a length range from about 0.5 micron to about 10 micron, andwherein the interstitial carbon nanotube heat transfer structures occupyfrom less than about 5 to about 30 volume percent of the thermalintermediate material.
 11. The apparatus of claim 10, wherein the matrixis a metal selected from the group consisting of indium or an indiumalloy.
 12. The apparatus of claim 11, wherein the carbon nanotubes aredecorated with metal.
 13. The apparatus of claim 12 wherein the metal isselected from the group consisting of platinum, gold, silver andpalladium and their alloys.
 14. A computing system, comprising: at leastone dynamic random access memory device; a die including a die surfaceand a circuit to electrically couple to the memory device; a heat sink;and a thermal intermediate structure interposed between the die surfaceand the heat sink and comprising a plurality of carbon nanotubes, someof which are decorated with metal and blended with solder.
 15. Thesystem of claim 14, wherein the circuit comprises a processor that actsupon data signals, and may include, for example, a microprocessor. 16.The system of claim 14, wherein the metal is one or more metals selectedfrom the group consisting of platinum, gold and silver and alloys of oneor more of platinum gold and silver.
 17. The system of claim 14 whereinthe solder is indium.